Semiconductor and micromechanical dies or chips are frequently packaged for protection against an external environment. The package provides physical protection, stability, external connections, and in some cases, cooling to the die inside the packages. Typically the chip or die is attached to a substrate and then a cover that attaches to the substrate is placed over the die. Alternatively, the die is attached to a cover and then a package substrate is formed on the die.
While there is a trend to add more functions to each die, there is also a trend to put more than one die in a single package. Since a package is typically much larger than the die that it contains, additional dies can be added without significantly increasing the size of the package. Current packaging technologies include stacking dies on top of each other and placing dies side-by-side on a single package substrate. Consolidating more functions into a single die and placing more dies into a single package are ways to reduce the size of the electronics and micromechanics in a device.
As wireless connectivity is expanded to more devices and the sizes of these devices are reduced, RF (Radio Frequency) packages are placed ever closer to digital and baseband packages. The digital and baseband packages typically generate noise and interference that can disrupt or impair the operation of the RF systems. At the same time, RF systems may generate radio interference that impairs the operation of the digital and baseband systems. As a result, the RF modem is typically shielded by a metal case that covers the package or is a part of the package to avoid interference from the digital circuitry. Such an external EMI (Electro-Magnetic Interference) shield is frequently placed over packages for cell phones, tablets, notebook computers, wireless routers, and other communication devices after the packages are surface mounted to a PCB (printed circuit board) for the device.